In some checkout systems of retail stores, an input processing apparatus for inputting commodity data and a settlement apparatus for settling a transaction are separated. The input processing apparatus waits for input of data relating to a commodity. If the data is input by an operator, the input processing apparatus generates settlement information based on the data and sends the settlement information to the settlement apparatus. The settlement apparatus waits for input of payment data for the settlement information. If the payment data is input by the operator, the settlement apparatus processes settlement on the basis of the settlement information and the payment data. Such a checkout system in which the input processing apparatus and the settlement apparatus are separated can adopt a so-called semi-self-service system in which a store clerk operates the input processing apparatus and a customer operates the settlement apparatus. In this kind of checkout system, there is a possibility of causing confusion to the customer who carries out the settlement if new settlement information is received by the settlement apparatus which is already executing the settlement processing. Therefore, the settlement apparatus receives new settlement information only in a case in which the settlement processing is not executed.
However, even if the settlement processing for one transaction is completed, it is not always true that a customer, i.e., a person that has settled the transaction, leaves the settlement apparatus quickly. Then, there is still a possibility of causing confusion to the customer if the new settlement information is received by the settlement apparatus that is kept in a state in which the customer who finishes the settlement still stands in front of the apparatus and the settlement apparatus is capable of starting the settlement processing for another customer.